1. Field of the Invention
The present invention relates to a print head used in an ink jet printer.
2. Description of the Related Art
There are two major categories of conventional dot-on-demand print heads for ink jet printers. One category includes print heads with thermal elements (that is, elements for converting electric energy to heat energy) and the other category includes print heads with piezoelectric elements (that is, elements for converting electric energy into mechanical energy). As is well known, thermal elements are used in print heads to directly heat the ink, or other material to be ejected from the print head, in order to generate a vapor bubble. Ink is ejected from nozzles in the print head by the force of expanding bubbles. Not all materials are well adapted for this heating process, so not all materials can be ejected from print head that use thermal elements.
No such restrictions exist for materials to be ejected from print heads that use piezoelectric elements. Print heads that use piezoelectric elements also have the advantage of being durable. On the other hand, print heads that use piezoelectric elements can not be produced using semiconductor production techniques. Therefore, print heads with piezoelectric elements can not be produced in as compact and integrated a form as print heads with thermal elements.
Japanese Patent Application Kokai No. HEI-2-150355 describes a print head wherein pressure for ejecting ink is generated using motion created when piezoelectric material deforms in the shear mode. The resultant print head has a compact and a highly integrated structure.
FIG. 1A shows an ink jet print head 1 described in the Japanese Patent Application Kokai No. HEI-2-150355. Directional terms such as "upper," "lower," "front," and the like used in the following explanations refer to the ink jet print head 1 when in the posture shown in FIG. 1A. The ink jet print head 1 includes a piezoelectric ceramic plate 2, a cover plate 3, a nozzle plate 31, and a substrate 41. The print head 1 is provided with a plurality of ink chambers 12 (see FIG. 5), each of which is defined by two adjacent side walls 11, the floor of a groove 8 defined between the two adjacent side walls, a surface of the nozzle plate 31, and a surface of the cover plate 3.
More specifically, the piezoelectric ceramic plate 2 is formed with a plurality of grooves 8 extending parallel to one another. As shown in FIGS. 1B, 1C and 2, each groove 8 includes a channel groove portion 17, a sloping groove portion 19, and a shallow groove portion 16. Metal electrodes 13, 18, and 9 are provided in connection in each groove 8. A metal electrode 13 is provided at the channel groove portion 17 of each groove 8 on the upper half of opposing side surfaces of two adjacent side walls 11 that sandwich groove 8 therebetween. A metal electrode 18 is provided at the sloping groove portion 19 of each groove 8 on the upper portion of opposing side surfaces of the two adjacent side walls 11 that sandwich groove 8 therebetween. The metal electrode 18 has the same width as the metal electrode 13. The metal electrode 18 is also provided to an upper portion of the floor of the sloping groove portion 19 of each groove 8. The metal electrode 9 is provided, at the shallow groove portion 16 of each groove 8, to completely cover the opposing side surfaces of the two adjacent side walls 11 that sandwich groove 8 therebetween and the floor of the shallow groove portion 16.
The substrate 41 is attached to the base of the piezoelectric ceramic plate 2. Conductor layer patterns 42 are provided to the substrate 41 at positions thereof corresponding to positions of each groove 8. Conductor wires 43 are provided to connect one end of each conductive layer pattern 42 with its respective metal electrode 9 formed at the floor of the shallow groove portion 16. As shown in FIG. 4, the other ends of the conductive layer patterns 42 are connected to an LSI chip 51 by wires. A clock line 52, a data line 53, a voltage line 54, and an earth line 55 are also connected to the LSI chip 51.
With this structure, the channel groove portion 17 and the sloping groove portion 19 of each groove 8, sandwiched between two adjacent side walls 11, defines an ink chamber 12 for being filled with ink. A pair of opposing side surfaces of the two adjacent side walls 11 defining each ink chamber 12 therebetween are provided with opposing metal electrodes 13 and 18. The metal electrode 18 is also provided in an upper portion of a floor of the sloping groove portion 19 of each ink chamber 12. Each shallow groove portion 16 is formed, at a portion close to an end 15 of the plate 2, in correspondence with each ink chamber 12 to be provided with a metal electrode 9 for electrically connecting each conductive layer pattern 42 to the opposing metal electrodes 13 and 18 provided at the corresponding ink chamber 12. It is noted that the sloping groove portion 19 is inevitably formed when the ink channel groove portion 17 and the shallow groove portion 16 for each ink chamber 12 are produced through dicing technique, as will be described below.
The following is an explanation of a method for manufacturing the ink jet print head 1. As shown in FIG. 2, the piezoelectric ceramic plate 2 is formed from a plate of lead zirconium titanate (PZT), a ferroelectric ceramic material, that is polarized in the direction indicated by the arrow 5. Grooves 8 are cut in the plate with a rotating diamond cutter blade 30 in a dicing technique. To form the channel groove portions 17, the sloping groove portions 19, and the shallow groove portions 16 in the grooves 8, the diamond cutter blade 30 is first caused to cut into the plate in the direction indicated by arrow 30A to form the channel groove portion 17. After the diamond cutter blade 30 travels in the direction indicated by arrow 30A for a predetermined distance, the cutting direction is changed to the direction indicated by arrow 30B, thereby reducing the cutting depth. The sloping portion 19 is formed at this time to a curved surface with substantially the same curvature as that of the diamond cutter blade 30. The cutting direction is then changed to that indicated by arrow 30C to form the shallow portion 16. Adjacent grooves 8 are separated by side walls 11, which are polarized in the direction indicated by arrow 5.
As shown in FIG. 1A, the piezoelectric ceramic plate 2 is thus formed with a plurality of grooves 8 all cut in parallel to an equal depth. The dimensions of the channel groove portions 17 and the shallow groove portions 16 are determined by the thickness of the diamond cutter blade 30 and the amount to which the diamond cutter blade 30 is set to cut into the plate. The pitch of the grooves 8 is determined by control of the feed pitch of the process table, and the number of grooves 8 is determined by the number of times the plate is cut. The curvature of the sloping groove portion 19 is determined by the radius of the diamond cutter blade 30. Because the process is commonly used in manufacturing semiconductors, extremely thin diamond cutter blades 30 with thickness of 0.02 mm are sold on the market. Therefore, the print head 20 can be made with sufficiently high integration.
As shown in FIG. 3, to form the metal electrodes 13, 18, and 9, the piezoelectric ceramic plate 2 with grooves 8 formed therein is tilted at an angle in relation to the direction B in which vapor travels from the deposition source (not shown). This tilt places one side wall 11 defining each groove 8 entirely in a shadow with respect to the direction B. The floor and the lower half of the other side wall 11 are also in a shadow at the channel groove portion 17. At the sloping groove portion 19, the lower portion of the other side wall 11 and the lower portion of the sloping floor are also in a shadow. Therefore, metal from metal vapor released in direction B deposits only on surfaces that are not in shadowed regions. As a result, a metal electrode 10 is formed on the top surface of all side walls 11; a metal electrode 13 is formed on the upper half of the unshadowed side of each side wall 11 at the channel groove portion 17 of each groove 8; a metal electrode 18 is formed on the upper portion of the unshadowed side wall 11 and the upper portion of the sloping floor at the sloping groove portion 19 of each groove 8; and a metal electrode 9 is formed on the unshadowed side of the side walls 11 and floor at the shallow groove portions 16.
Next, the piezoelectric ceramic plate 2 is rotated 180 degrees and metal electrodes 13, 18, 9, and 10 are formed on opposite side walls, and the like, in the same manner. The metal electrode 10 are then removed from the top of the side walls 11 by lapping or other similar technique. As mentioned previously, the metal electrode 18 of each groove 8 electrically connects the corresponding metal electrode 13 to the corresponding metal electrode 9.
To form the cover plate 3 shown in FIG. 1A, a plate of a resin material, a ceramic material, or other suitable material is cut or ground to form an ink introduction portion 21 and a manifold 22 therein. Then, the side of resultant cover plate 3 with the manifold formed therein is adhered, using an adhesive 4 such as epoxy (see FIG. 5), to the side of the piezoelectric ceramic plate 2 with the grooves formed therein. When covered, the grooves 8 form a plurality of ink chambers 12 (see FIG. 5) which are separated from each other in the horizontal direction at an interval determined by the thickness of the side walls 11.
The nozzle plate 31 is formed from a plastic plate made from polyalkylene terephthalate (for example, polyethylene terephtalate), polyimide, polyether imide, polyether ketone, polyether sulfone, polycarbonate, cellulose acetate, or similar plastic. Nozzles 32 are opened in the nozzle plate 31 at positions thereof corresponding to the positions of the ink chambers 12. The nozzle plate 21 is adhered to the end of the cover plate 3 and the piezoelectric ceramic plate 2 nearest the channel groove portions 17.
The conductor layer patterns 42 are formed in the substrate 41 at positions thereof corresponding to positions of each ink chamber 12. Wire bonding or other similar well-known technique is used to connect conductor wires 43 between conductive layer patterns 42 with respective metal electrodes 9 formed at the floor of the shallow grooves 16. The substrate 41 is then adhered, using an adhesive such as epoxy, to the side of the piezoelectric ceramic plate 2 without grooves 8 formed therein.
Next, an explanation of the operation of the ink jet print head 1 will be provided while referring to FIGS. 5 and 6. All of the ink chambers 12 are filled with ink. The clock line 52 consecutively supplies a clock pulse. Based on the clock pulse and data incoming over the data line 53, the LSI chip 51 determines from which ink chambers 12 ink is to be ejected. In regards to an ink chamber 12 from which is not to be ejected, the LSI chip 51 applies a ground voltage 0 V from the ground line 55 to the metal electrodes 13 of the ink chamber 12 via the corresponding conductive layer pattern 42 and metal electrodes 9 and 18.
In regards to ink chamber 12b from which ink is to be ejected, the LSI chip 51 applies a positive voltage V from the voltage line 52 to the metal electrodes 13e and 13f via the conductive layer pattern 42 and the metal electrodes 9 and 18 that correspond to the ink chamber 12b. At the same time, the LSI chip 51 applies a voltage 0 V from the ground line 55 to the metal electrodes 13d and 13g via the conductive layer patterns 42 electrically connected to metal electrodes 13 of ink chambers 12 that are not to be driven. As shown in FIG. 6, an electric field is generated in the side wall 11b the direction indicated by arrow 14b, and an electric field is generated in the side wall 11c the direction indicated by arrow 14c. Because the electric field directions 14b and 14c are at right angles to the polarization direction 5, the side walls 11b and 11c rapidly deform toward the interior of the ink chamber 12b by the piezoelectric shear mode effect. The volume of the ink chamber 12b reduces as a result, and pressure rapidly increases so that an ink droplet with a predetermined volume is ejected at a predetermined speed from the nozzle 32 connected to the ink chamber 12b.
When application of the drive voltage V is stopped, the side walls 11b and 11c revert to their condition before deforming (see FIG. 5). Ink pressure in the ink chamber 12b drops as a result so that ink is drawn into the ink chamber 12b from the ink introduction port 21 and the manifold 22.